My reasons for saying that Commercial Crew vehicles are too small is that I think we have learned that for humans to stay healthy in space that they need a lot of room, so future human space travelers are not going to be spending most of their time in a capsule like the Dragon or CST-100. Plus, capsules are really only designed for transporting humans to/from a planet with an atmosphere, so at most my view is that if we take them BEO it's only for use as a lifeboat and for the "last mile" of getting humans down onto a planet. And currently the only planet we know we can land them as currently designed is Earth, so why not leave them orbiting in LEO and just plan to meet back up with them in Earth orbit on the way back?

I envision for Commercial Capsule's some type of mission module that the capsule will dock to after launch similar to how the Apollo CSM docked to the LM after TLI. The mission module will be fairly light structurally since it isn't intended for re-entry. Could be even a Bigelow inflatable. The module will be discarded shortly before re-entry into Earthís atmosphere.

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"Look at that! If anybody ever said, "you'll be sitting in a spacecraft naked with a 134-pound backpack on your knees charging it", I'd have said "Aw, get serious". - John Young - Apollo-16

My reasons for saying that Commercial Crew vehicles are too small is that I think we have learned that for humans to stay healthy in space that they need a lot of room, so future human space travelers are not going to be spending most of their time in a capsule like the Dragon or CST-100. Plus, capsules are really only designed for transporting humans to/from a planet with an atmosphere, so at most my view is that if we take them BEO it's only for use as a lifeboat and for the "last mile" of getting humans down onto a planet. And currently the only planet we know we can land them as currently designed is Earth, so why not leave them orbiting in LEO and just plan to meet back up with them in Earth orbit on the way back?

I envision for Commercial Capsule's some type of mission module that the capsule will dock to after launch similar to how the Apollo CSM docked to the LM after TLI. The mission module will be fairly light structurally since it isn't intended for re-entry. Could be even a Bigelow inflatable. The module will be discarded shortly before re-entry into Earthís atmosphere.

Need to get over the 'discard after use' concept... is there any reason that an inflatable could not autonomously aero-break into a HEO and await reuse? The capsule could be separated and reenter while the aero-breaking of the mission module begins. We're not going anywhere if we cannot get past leaving debris trails along each mission's flight path.

Need to get over the 'discard after use' concept... is there any reason that an inflatable could not autonomously aero-break into a HEO and await reuse? The capsule could be separated and reenter while the aero-breaking of the mission module begins. We're not going anywhere if we cannot get past leaving debris trails along each mission's flight path.

I would think a careful look at cost would be in order. What would be the additional mass required to have a "mission module or inflatable" be able to aero-break in a HEO while coming back from a BEO manned mission considering the velocities involved. Not saying it is impossible but this needs to be looked at. Also the "mission module or inflatable" if it was going to be re-used for another mission would have to refurbished and re-stocked with supplies. It might be cheaper to just create a disposable mission module for each BEO mission especially if the price per kg to orbit continues to drop. The disposal might also depend on the mission. For a lunar mission the "mission module or inflatable" might be re-usable since it doesn't need to be occupied for very long. For a Mars mission you might want to dispose of it after use. You could very well have new forms of mold etc. growing inside.

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"Look at that! If anybody ever said, "you'll be sitting in a spacecraft naked with a 134-pound backpack on your knees charging it", I'd have said "Aw, get serious". - John Young - Apollo-16

I would think a careful look at cost would be in order. What would be the additional mass required to have a "mission module or inflatable" be able to aero-break in a HEO while coming back from a BEO manned mission considering the velocities involved. Not saying it is impossible but this needs to be looked at.

Now doubt there is a lot that we still need to work out to implement a reusable transportation system. NASA has been wanting to invest in some of technologies we'll need, and some is being done in private industry, but it certainly needs more work.

So in the near-term the cheaper solution will likely involve throwing away perfectly good hardware, and that is going to barrier to doing more in space because we are not able to lower the costs fast enough.

To change this is going to require a change in mindset, and the willingness of Congress to allow NASA to help perfect a number of needed technologies. But based on the spending priorities Congress currently has I'm not sure when NASA will be able to help with this challenge, so that leaves it up to the private sector.

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If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Sure, but that doesn't mean choosing direct return to Earth is an example of the Apollo paradigm.

To me Apollo was an example of a completely disposable architecture, which makes it hard to scale up.

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I see the most promising path as commercial transport to a commercially operated LEO way station, followed by commercial transport to a waiting NASA MTV based at L1/L2 (using as many commercially available components as possible, such as Bigelow habs) which is supplied by commercially operated tankers at L1/L2, Sun Mars L1/L2 and Phobos / Deimos / LMO. Eventually, there could also be commercially operated way stations at L1/L2, Sun Mars L1/L2 and Phobos / Deimos / LMO.

Aerobraking back to LEO is very difficult...

Today, sure. But we also haven't been trying very hard to solve this. I know Jon Goff has some insight into possible technologies that could help solve this, which I think include Magnetic Aerobraking. But this does need attention and funding to figure out what the best solution is.

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...propulsive return to LEO is expensive...

Again, today, sure. But if a certain space transportation company is able to perfect some form of reusability, then in-space fuel costs will be able to drop significantly. So really the solution for this one is based on supply & demand costs for fuel, because once they get down low enough then we can start reusing spacecraft.

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...while propulsive return to L1/L2 and direct return from L1/L2 to Earth are both cheap and straightforward. I don't see much benefit from changing to a separate LEO capsule for return, especially since the return capsule from L1/L2 can be a properly modified Dragon or CST-100.

Today that works, and for a limited number of people. The challenge is that such a system doesn't scale well, and if we're not scaling then we are not going to be able to do all the things we'd all like humanity to do in space.

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If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Now doubt there is a lot that we still need to work out to implement a reusable transportation system. NASA has been wanting to invest in some of technologies we'll need, and some is being done in private industry, but it certainly needs more work.

So in the near-term the cheaper solution will likely involve throwing away perfectly good hardware, and that is going to barrier to doing more in space because we are not able to lower the costs fast enough.

To change this is going to require a change in mindset, and the willingness of Congress to allow NASA to help perfect a number of needed technologies. But based on the spending priorities Congress currently has I'm not sure when NASA will be able to help with this challenge, so that leaves it up to the private sector.

I think people would be surprised at how much lower the costs would be for some type of standard production "Mission Module". Most of the expensive parts stay in the capsule and the "Mission Module could be fairly simplified. What really gets costs cranking for NASA is that they have to do a one-off design and getting the mass into orbit. If you had to design a new mission module from scratch every time you flew one then the costs would be fairly high. However if you designed a standard module and then just kept building to that standard design your costs come down a lot. You then place that with lower costs to orbit you get something that could dramatically lower prices. Not enough to get into the 1/2 Million dollars to Mars cost that Musk wants but enough to be a good start until more re-usability is figured out.

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"Look at that! If anybody ever said, "you'll be sitting in a spacecraft naked with a 134-pound backpack on your knees charging it", I'd have said "Aw, get serious". - John Young - Apollo-16

Today that works, and for a limited number of people. The challenge is that such a system doesn't scale well, and if we're not scaling then we are not going to be able to do all the things we'd all like humanity to do in space.

I think the only part that wouldn't be reusable would be the SM of the capsule. I suspect that could be made reusable later, and that aerobraking just a SM is easier than a whole capsule. But I wouldn't like it to be the first step, since I think it's too ambitious. As for a very ambitious long-term plan, I think NASA's OASIS architecture was very nice, except for the fact that it saw all in-space elements as traditional NASA projects, rather than commercial-crew-like competitive procurement of resupply services.

Need to get over the 'discard after use' concept... is there any reason that an inflatable could not autonomously aero-break into a HEO and await reuse? The capsule could be separated and reenter while the aero-breaking of the mission module begins. We're not going anywhere if we cannot get past leaving debris trails along each mission's flight path.

If we are not too worried about return time we could use an ion thruster. Low thrust EML-1 to LEO is a delta-v of 7.0 km/s using an Isp of 5000s.

Today that works, and for a limited number of people. The challenge is that such a system doesn't scale well, and if we're not scaling then we are not going to be able to do all the things we'd all like humanity to do in space.

I think the only part that wouldn't be reusable would be the SM of the capsule. I suspect that could be made reusable later, and that aerobraking just a SM is easier than a whole capsule. But I wouldn't like it to be the first step, since I think it's too ambitious. As for a very ambitious long-term plan, I think NASA's OASIS architecture was very nice, except for the fact that it saw all in-space elements as traditional NASA projects, rather than commercial-crew-like competitive procurement of resupply services.

Dragon shouldn't need a service module just for entering and exiting EML1/2. All you'd have is the trunk, and even that could be gotten rid o with a clever folding solar array (and/or small radiator) in the nose and/or better Li-S batteries (which are just as good as fuel cells).

Chris Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

In terms of going to and from the region of the moon direct reentry to earth would probably be the best bet. It costs less in delta V and you get your vehicle back on the ground where it can be inspected and reused(in theory).

To me that's like saying all Boeing aircraft would have to land in Everett WA to be inspected and refueled after every flight. It's hard to scale a transportation system like that.

Sure breaking it into segments is what happens here on earth but not everything needs to be carried the same way. On earth the jetís fuel could be a carried by pipeline, tanker, rail car and truck to the airport and the Jet carrying passengers could fly in deposit passengers pick up some more passengers refuel and fly further. In fact moving fuel by air is not cost effective and used only when there is no other option to do so.

The problem with transporting people in space vs. cargo is that the first needs a fast trip while the latter could benefit from slower trips. The problem is that returning to LEO with a crew is very hard. Some methods like SEP and aero braking are just too slow or in the case of aero braking too many passes through the Van Allan belts for crew. And some cargo like fuel is time insensitive and you could send more by slower trips.

The crew really could travel in something like a capsule or a lifting body designed to be deposited in LEO, transferred to L1/L2 and renter to earth. A transfer stage could be used to push the capsule out. It could be fueled in LEO and push the capsule or other cargo that needs a fast trip to L1/L2. It would be returned to LEO unmanned by some hopefully cost effective means like SEP and refueled there by some cost effective means. The capsule would reenter from L1/L2.

If we can get reusability up to LEO then the rest could follow. At the moment part of the problem is being worked on Dragon and first stage reuse. Something like Dragon could cover LEO to L1/L2. It is really only when you start to leave earth orbit that direct reentry or carrying the capsule with you becomes debatable.

Dragon shouldn't need a service module just for entering and exiting EML1/2. All you'd have is the trunk, and even that could be gotten rid o with a clever folding solar array (and/or small radiator) in the nose and/or better Li-S batteries (which are just as good as fuel cells).

What is type of engine is providing the Delta-V change for entering/exiting EML1/2?

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"Look at that! If anybody ever said, "you'll be sitting in a spacecraft naked with a 134-pound backpack on your knees charging it", I'd have said "Aw, get serious". - John Young - Apollo-16

Dragon shouldn't need a service module just for entering and exiting EML1/2. All you'd have is the trunk, and even that could be gotten rid o with a clever folding solar array (and/or small radiator) in the nose and/or better Li-S batteries (which are just as good as fuel cells).

What is type of engine is providing the Delta-V change for entering/exiting EML1/2?

The Falcon Heavy can throw the Dragon to EML-1/2, so the RCS can do the docking.

The CST-100 (Mark 2) would need a transfer stage to go fro LEO to EML-1/2. As the spacecraft is in orbit a medium thrust vacuum engine is sufficient. Candidates include the hydrogen/LOX RL10 engines on the Centaur or the methane/LOX Morpheus HD5 engines or the monomethylhydrazine Space Shuttle OMS engines. Possibly modified for a longer burn.

Dragon shouldn't need a service module just for entering and exiting EML1/2. All you'd have is the trunk, and even that could be gotten rid o with a clever folding solar array (and/or small radiator) in the nose and/or better Li-S batteries (which are just as good as fuel cells).

What is type of engine is providing the Delta-V change for entering/exiting EML1/2?

Dracos, of course. Remember, Orion had thrusters as backup to its OMS engine, and that was for lunar orbit. Certainly not Superdracos. Remember, Dragon launches with all that abort propellant which it could use (if it doesn't have enough prop for full vertical landing back on Earth, it may still have enough for parachute assist), and one could imagine a slight increase in propellant. You'd need about 500m/s or so, depending on just how fast of a transit you want. If you can afford to wait, you need a lot less propellant.

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Chris Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Short answer, there are two classes of approaches to using magnets and plasmas for aerobraking or aerocapture. The one linked to above uses plasma generated due to the bow shock created while your spacecraft passes through the atmosphere. With a strong enough magnet, as the partially ionized gas flows around your vehicle, the conductivity of the gas and the magnetic field interact to create a current loop in front of the vehicle, which pushes the bow shock back away from your vehicle. The magnetic pushback enhances your drag force, and reduces the plasma density in the bowshock (lowering dynamic pressure and heating). But it requires a pretty strong magnet, and only works when you're going fast enough to ionize enough of the incoming air.

The other approach is the stuff we're working on with MSNW. In this approach, you get create a low-density seed plasma and capture it with a weaker electromagnet around your spacecraft. As neutral gas passes into the plasma, charge exchange collisions ionize the neutrals, which are then captured by the electromagnet.

Of the two, I'm more of a fan of the MSNW approach, as it requires less exotic magnets, works at a wider velocity range, and operates at a higher altitude range with lower effective ballistic coefficients.

But one of the key things about either of these technologies, is that they enable you to now start non-propulsively recovering and reusing spacecraft in LEO. If MAC works and scales up, you should be able to brake or capture something that is completely unaerodynamic (Bigelow module, Centaur stage, space station, etc) into LEO with a fairly low mass hit, and no propellant required. If it's easy to stop in LEO like that, you no longer really need to lug a capsule around, and you can start reusing in space hardware.

Dragon shouldn't need a service module just for entering and exiting EML1/2. All you'd have is the trunk, and even that could be gotten rid o with a clever folding solar array (and/or small radiator) in the nose and/or better Li-S batteries (which are just as good as fuel cells).

As I understand it, it is possible to create a Magnetic Sail that would allow a craft to lift itself out of Earth orbit, via the planet's magnetic field. (I read one article that suggested it may be possible to launch from teh Earth's surface with a Magnetic sail, but I think thats a bit far fetched).

What I was suggestion was, as a craft is returing to Earth, use a magnetic sail as a sort of "deep space parachute" to bleed off eneough velocity of the entire craft, (Mars mission craft, habitats, engines, etc.) so that the entire craft can make orbit around the Earth and teh ERV Capsule would only have to resist the reentry from LEO rather fronm a high velocity BEO return.

Obviously, using susch a system to achieve Mars orbit would be impossible, due to teh practically complete absense of a Martian magnetic field, therefor aero braking becomes a necessity.

It also occures to me that a craft using a nuclear rocket is likely to also be suing some sort of Magnetic shielding to protect teh crew from solar and nuclear radiation. If so, it may be possible to use this shield as a Magnetic sail to give the craft an additional boost via Earth's Magnetic field.

As I understand it, it is possible to create a Magnetic Sail that would allow a craft to lift itself out of Earth orbit, via the planet's magnetic field. (I read one article that suggested it may be possible to launch from teh Earth's surface with a Magnetic sail, but I think thats a bit far fetched).

What I was suggestion was, as a craft is returing to Earth, use a magnetic sail as a sort of "deep space parachute" to bleed off eneough velocity of the entire craft, (Mars mission craft, habitats, engines, etc.) so that the entire craft can make orbit around the Earth and teh ERV Capsule would only have to resist the reentry from LEO rather fronm a high velocity BEO return.

Obviously, using susch a system to achieve Mars orbit would be impossible, due to teh practically complete absense of a Martian magnetic field, therefor aero braking becomes a necessity.

It also occures to me that a craft using a nuclear rocket is likely to also be suing some sort of Magnetic shielding to protect teh crew from solar and nuclear radiation. If so, it may be possible to use this shield as a Magnetic sail to give the craft an additional boost via Earth's Magnetic field.

Jason,

I was replying to both of you (Ron PM'd me to see if I would jump into the conversation).

Re: magnetic sails...I don't know what you're talking about. Earth's magnetic field force is way too weak to push against to perform capture maneuvers. Maybe you're thinking of the theoretical work done on "M2P2" magnetosphere sails that deflect the solar wind as way of generating tiny amounts of thrust--comparable to a solar sail. Maybe you're thinking of that? You might be able to very gradually capture into a high orbit around earth, but spiraling in would take forever. And M2P2 requires very high magnetic field strengths, superconducting electromagnets, etc.

You could achieve the end you're talking about (capturing an interplanetary exploration "vehicle"/assembly into LEO) much easier with the Magnetoshell Aerocapture technology I described above. The MSNW guys working on MAC work with some of the UW guys who did M2P2, but MAC is a much simpler technology that I think is a lot closer to being flight ready. It would allow you to brake an entire mission stack into LEO (likely you'd do a capture pass than 2-10 braking passes to keep the delta-V you need in a given pass to a reasonable level), and you would only need an electromagnet (preferably on a deployable structure of some sort), some batteries, and the plasma generator.

Electrodynamic tethers (EDTs) are long conducting wires, such as one deployed from a tether satellite, which can operate on electromagnetic principles as generators, by converting their kinetic energy to electrical energy, or as motors, converting electrical energy to kinetic energy.[1] Electric potential is generated across a conductive tether by its motion through a planet's magnetic field.